Can't change mouse influence in proportional editing mode
I'm adding an answer here because effected users might overlook what is written in the comments:

If you're working with large scale models to scale (say at a distance 100Km), the influence radius will likely be too small for you to notice, even if you scroll multiple times. When you grab (G) a vertex or edge, press the page up key and keep it pressed until the scope starts to become visible. "proportional size" at the bottom of your 3D view might appear to not change, but it eventually will.

Hope this spares another soul some misery.